Awatoto flooding. Photo: Florence Charvin

The latest round of test results show high levels of e.coli from faecal contamination in silt, rather than from chemicals said Napier City Council spokeswoman Jess Soutar Baron.

Residents impacted by the contamination at Awatoto are receiving individualised reports based on council silt testing. Private bores have also been tested and paid for by the council.

Preliminary tests done in February had shown even the samples with the lowest faecal coliform was more than 110 times over official safe standards.

Test results had been similar for industry – high levels of e.coli were the primary concern – but each business was doing its own silt testing at their sites, and when complete those results would be sent to the council.

“Depending on what’s in it we will either take it to the holding site and treat it or it will be taken off site,” Soutar Baron said.

“We are developing a temporary silt holding site on land owned by the council next to the Napier wastewater treatment plant. It will be ‘bunded’ which means it has a mounded wall around it. 

“It will have a membrane that lets water out but keeps silt in. Silt will be compacted and covered and we will use dust suppression methods. We are using ambient monitoring units to monitor the air at the site.”

Silt that is contaminated with high levels of e.coli will be treated with hydrated lime, and ongoing degradation tests will be carried out on the silt, she said.

It was currently degrading at a rate of 60% a week.

Some residents had expressed concern that contaminated silt had simply been moved off their property to a nearby site, but the council is satisfied safety won’t be an issue.

Soutar Baron said the bunding and membrane were RMA compliant and groundwater results had come back “very reassuring”. The site was more than 30 metres from the water way and dust monitoring showed no significant impacts for the creation of the storage area.

“We have engineers and environmental scientists working hard on it and we are guided by advice from a number of experts like WorkSafe and Te Whatu Ora. We will be monitoring it closely and testing regularly.”

What is being tested for

The latest test results have not been published so we still don’t know what the concentrations are, however, BayBuzz was provided with a list of contaminants that the council was screening for.

These included tests for microbiology, organics and pH such as faecal coliform, e.coli, ammonium-N, Nitrate-N and Nitrite N.

Heavy metals were tested for – arsenic, cadmium, chromium, copper, lead, nickel and zinc, as were petroleum hydrocarbons, asbestos, pesticides such as dieldrin, DDT, acid herbicides and PCBs.

The council also confirmed businesses within the area had been asked to provide an inventory of chemical loss to the council so it could understand what kind of chemicals and potential contaminants might have been washed out in the flood. These have yet to be returned to council.

Auckland University associate professor of environmental engineering, Lokesh Padhye said the contaminants listed were commonly tested contaminants, and made sense given the types of industry located in Awatoto, such as the Ravensdown factory.

Last week BayBuzz asked him to review the preliminary findings from the first tests taken in February. Padhye said based on the limited information available at the time – which excluded what was being tested for and what concentrations were showing up – that the biggest concerns were faecal contamination, which continues to be the biggest concern, and ammonia.

Padhye said ammonia, especially if it is converted into nitrites can be very dangerous. If it gets into waterways it can kill aquatic life, although it generally gets diluted very quickly, and if consumed in drinking water it can prevent red blood cells from taking up oxygen. 

“That’s why there are maximum contamination levels of nitrites and nitrates in drinking water.”

In surface water they can cause algal blooms and produce toxins, he said.

comparable analysis has also been provided by NIWA aquatic scientist Jennifer Gadd.

Soutar Baron confirmed that chemical sampling of private bores had taken place on 16, 17, 20 and 21 March and results were due back on 31 March. Te Whatu Ora had recommended that residents drink bottled water until results came back clear.

“Most biological results came back clear. There are some private bores which have e.coli in them. Private drinking water bores fall under the jurisdiction of Taumata Arowai and owners work closely with them on mitigation and treatment processes,” Soutar Baron said.

Public interest journalism funded by New Zealand on Air.


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